Characterizing pozzolanic activity of rice husk ash by impedance spectroscopy

The present work aims to use impedance spectroscopy to characterize pozzolanic activity of RHAs prepared on a pilot scale. The method is based on the rate of the normalized conductivity change of the Ca(OH)2 + RHA paste, d(σ/σ0)/dt, during the first 24 h of hydration. The measurement was found to be sensitive to the unburnt carbon content in the 6-8 wt.% range and the amorphous SiO2 content (regardless of the unburnt carbon content). When used to evaluate two separate groups of RHAs, each with comparable unburnt carbon contents, the method gives very high correlation coefficients to the strength activity index at 3, 7, and 28 days. However, the correlation coefficients fall significantly when RHAs with vast difference in the unburnt carbon contents are considered together. The method thus proves to be powerful for evaluation of the pozzolanic activity of RHAs with comparable carbon contents.